Method of and apparatus for control of liquid-fuel burners



R. F. METCALFE A METHOD OF AND APPARTUS FOR CONTROL OF LIQUIDr FUEL BURNERS Filed May 6. 1926 um Nv Q N u uw -wm w wlw .kww m. AN mw mw @5f l d B. w E. .i.\1. ll .il m k Mh., nu m .ww wh w m. .mw l n Patented oct. 16, 192s.

l I 1,688,126A f UNITEDSTATES PATENT oFF1cE.-

ROBERT F. METCALFE, OF BROOKLYN., NEW YORK, ASSIGNOR TO SOCONY BURNER CORPORATION, OF NEW YORK, N. Y., A CORPORATION OF DELAWARE.

METHOD OF AND APPARATUS FOR CONTROL OF LIQUID-FUEL BURNERS.

appiication inea May e, 192e. serial No. 107,112.

This invention pertainsvto a new and novel method, and the means therefor, for electrically controlling the operations of an apparatus.. y

In particular the invention has to do with the utilization of the variations in the conditions of gases at a definite location in an apparatus for the purpose of varying the electricalcontrol of the apparatus.

My invention, in one of its particular uses, will be described as being applied to and incorporated in a liquid fuel burner especially adapted for use in homes, and apartments and, in industrial work, to the heating of heat treatment furnaces, chemical vats and the like. It is to be understood that my invention may also be employed in other apparatus and for other like uses.

I-have discovered that there is a variation in the response' to the passage `of electrical current through a mixture of gases within a combustion chamber of a liquid fuel burner', before combustion takes 'place and after combustion tak/es place. M

In my discovery and in providing suitable electrical and mechanical apparatus responsive to these variations, I found that the automatic operation of a fuel burner may be controlled in a novel and improved manner to accomplish an efficient operation and to thereby assist in eliminating frehazards and f such burners.

dangers to persons, -apparatus and buildings.

It is well known that automaticallyl operating fuel burners have been in'use for a considerable period of time. It is also well known that the use of liquid fuel, such as lighter weight oils, have been employed in It has long been recognized that some part ofthe automatic control of such burners is responsive to a heat condition atsome definite point. It is desired to combine with such control an improved means to increase the efficiency of operation of such burners in that theywill automatically be fully stopped if ignition of the fuel does not take place when the burner starts up, or when there is a cessation of combustion of the fuel after the original ignition has been accomy pushed. i

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This invention, therefore, has as its main object the provision of a novel method of operation and desirable means for controlling an apparatus by utilizing the variations in the composition of gases at some predetermined point in theapparatus.

' liquid fuel burner with a heat absorbing devlce such as a boiler It is also an object of this invention. to provide a novel and improved control means which cooperates with other control yfeatures of an automatic fuel burner and which is responsive to the conditions of the gases within the burner or in a furnace in which the burner is placed or in the stack leading from the furnace.

It-is -a further object of my invention to provide a cooperating control means which is subject to being varied by reason of the electrical conductivity ofgases within the burner.

A particular object of my' invention is to provide an improved control for a liquid fuel burner whereby the variations in the gases which pass between the -points of a spark ignition plug are utilized `to maintain the burner in operation or to stop the burner.

Other objects and advantages of my invention will be appreciated asthe detailed description set forth below is read.

Whilethe invention hereinafter disclosed in detail has been shown as applied to a fuel burner constructed to operate on liquid fuel which develop in the burning of coal. Also l,

the position of the responsive means may be within the burner itself, within the' furnace with which the burner is associated or in the stack leading .from the furnace, or in any other desirable position where its function will be carried on.

The preferred manner in which I desire to disclose my invention is herein shown in the accompanying drawing representing. a liquid fuel heating system, and in this drawing Fig. 1 is a diagrammatic view of the preferred form of electrical control showing a furnace and a burner associated th/erewith and an enlarged portion of the burner, all combined with certain safety means;

Fig. 2 is an enlarged view of one of the safety devices taken on the line 2-2 of Fig. 1, and

Fig. 3 is an enlarged view of a desirable form of safety switch shown in diagrammatic form in Fig. 1.

' Referring now to the drawing, a suitable 1 is shownk in association or furnace 2V which in turn is provided with a suitable flue or stack 3. A combustion chamber 4 of the burner is shown in section in Fig. 1 and the burning of the fuel may be totally or partially accomplished within this combustion chamber. A suitable Vpipe 5 provides for the introduction of the fuel with air to support combustion into the usual cone 6. The combustible mixture preferably consists of oil and air in the form of gases and is preferably ignited bythe passing of sparks between the electric contacts 7 and'8 which usually form parts of a spark-plug. It has beenyfound desirable to mount the spark-plug in the cone 6.

The fuel burner 1 is usually provided with some means of operation and in this instance I have provided a suitable motor 9 which performs the functions of supplying oil and air -to the pipe 5 and supplying a supplementary amount of air through an opening 19350 that the complete combustion of the oil may be obtained for the purpose of heating the water or air within the furnace 2.

Any suitable means may be provided for controlling the operation of the liquid fuel burner,'but I have found it desirable toprovide an electrical control system'. I, therefore, provide electrical supply lines 11 and 12 having a suitable indicating lamp 14 placed across the lines at a` point between a fusible link 15 anda suitable snap switch in order to note that there is a proper supply of electricity. Usually this supply is of 110 volts as taken from the house supply lines. The line4 12 passes through a safety device preferably in thc` form of a fusible link l15 (Fig. 2) mounted in the liue of the boilery 2. The electrical supply lines pass through a suitable snap switch to terminal posts 16 and A17. 7

One circuit of the control system, which may be designated as a subelectricalcircuit,

on contact 26.

comprises leads 18 and 19` which are connect' ed to ay primary Winding 2O of a suitable transformer'21. Connected in the lines 18 and 19 is an electro-magnet or relay 22, the

`operation of which will hereinafter be del scribed.. From the secondary winding 23 of the transformer 21 an electrical conductor 24 leads to a contact 25, which is normally closed A conductor 27 leads to av lioat switch 28 and from there by means of conductor 29 to contact 30 which cooperates with a moving part Slot a suitable thermostat that may be located nearathe boiler'2 or at any desirable place in the home. A conductor` 32 leads to the usual aquastat 34 mounted in the boiler'. A conductor 35 leads from the other side of theaquastat to an electro-magnet 36 which in turn is connected to the other side of the secondary winding 23 of the transformer 21.

The `ioat feed switch 28 is adapted to open the control when the supply of liquid lfuel,

such as-oil, is either toohigh or too low. If proper it is usually found that an explosive mixture is fed to the combustion chamber 4 of the burner and this ioat switch 28 prevents the starting of the burner unless the proper supply of liquid fuel is available. The aquastat 34 operates to open the circuit in the event there is a dangerous low water condition in the boiler '2. It is Well understood that the aquastat may be supplemented by a pressure device which will open the circuit when the pressure of steam'I y burner and the burner wou-ld continue in op eration until the thermostat opened due to the desired amount of heat having been supplied.

The contacts 25 and 26 are normally in engagement and I have preferred tomount con- 'tact 25 on the free end of a metallic member which member will automatically move to separate contact 25 from contact 26 when the metallic member 37 has become heated to a predetermined extent aswill be hereinafter described. The separation of contacts 25 and 26 will likewiseprevent the starting of the burner when the thermostat 31 normally closes, or if during the running of the burner these contacts should beA Opened the burner will be automatically stopped.

A secondsubcircuit leading from theter- \minal posts 16 and 17 consists of a lead 38 which passesthrongh a field winding 39 oi the burner motor 9 and through the conductor 40 to a winding 4ljwhich is associated with the metallic member 37. It is preferred to place this Winding 41 around the metallic l member as illustrated in 1, although it may be associated in any other desirable form.

An electrical conductor 42 leads from'the other end of the winding 41rto a contact 44 which is adapted to be engaged by a contact 45 carried 0n an arm 46 which in turn is iniuencedby the magnet or relay 36. A conductor- 47 leads from the contact 45 to terminal post 1 6. e

Apart of `this invention consistsfin providing some nieansffor holding winding 41 out of circuit duringncrmal operation. In

accomplishing this endV Ikhave provided ashunt circuit around the .winding 41 associated with the metallic member 37.,` and in providing this shunt circuit a conductor 48 leads from conductor 42 to a flexible contact carrying member 49 preferably pivoted at 50 and having its freeend provided with acontact 51 which engages a 'suitably mounted .contacty 52 which in turn is connectedby' a conductor 54 .that leads to the conductor 40. Another' electrical' subci'rcuit of -tlie control system' is that illustrated by conductor 55 which leadsfrom terminal post 17 to the primary winding 56 of ay spark coil transformer.

A suitable conductor 57 leads from the other end of wlnding 56 toa magnet or relay 58 and heat responsive means.

from there conductor 59 leads to contact44. When the contacts 44 and 45 are closed the spark coil winding 56 and the magnet 58 are connected to the-other side of the supply line at terminal post 16 by means of conductor 47.

The safety device in the flue or stack as illustrated by the fusible link 15 is providedto open the electrical supply circuit in case of failure of aquastat 34, or when the water has been boiled out of the boiler or furnace 2, for under those conditions it will be seen that there will be no water in the boiler to absorb the heatand thus there will be an excessive amount of heat passing through the flue. This excessive heatacts to fusethe link 15 and open the electrical supply circuit thereby stopping'the operation of the burner. means for accomplishing the same end may be employed. c

.The metallic lmember 37 illustrated in detail in Fig. 3 may be anydesiredtype of venience I have called ita metallic member. Preferably it consists of two strips bf metal which have different coefficients of expansion and they are fastened together sothatupon being heated the metallic-member will automatically bend and its free end will rise; Since the free end carries contact 25 it will bey seen that this contact` will be carried away from contact 26. Other types of circuit opening heat responsive means may be em= p loyed if desired.

Inorder to prevent the movement of the metallic member 37 unless the actual desired conditions for its movement ,exist, I have herein provided a suitable means for maine taining the member 37 in its normal position. This preferred-means consists of a catch 60 having a suitable handle 61.' When the metallic member 87 is in its normal position this catch engages, preferably` by friction, the end of thatmember andis forced somewhat out of its normal position. When the metallicmember 37 is heated and bends it overcomes the frictional engagementbetween `it andthe `catch 60 and passes out of engagement with the catch 60. It will be noted from Fig. 3 that the catch will then move to the j left and upon the cooling of the member 37 the catch prevents' this member from return- ,'ing to its normal position that permits contact25 to engage contact- 26. It is desired thata manual operation beperformed to reset this switch. This operation is accomplished by movingy the `catch 60 by grasping its handle 61 and pulling it somewhat to the right and thus permitting the contact 25 to return to engagement with contact 26. Thus the preferredsafety switch consists of the metallic member 37 with its yarious elements and it may be-returned to its normal operating position by a suitablemanual movement. The manual movement may besubstituted If desired, another-type of safety rFor matter of con-V The Aresistance in this.V inployed for igniting the combustible mixture.

It is to be understood, however, that I may, in addition to the presence of a spark-plug, introduce two other contacts within the combustion chamber 4 and connect t em suitably in the electrical control system so that the system may be varied due to the resistance to passage of sparks between thecontacts and to causel the control system to close down orstop the burner when the resistance to the passage of the sparks continues for alength of time' sufficient to cause the heat responsive safety switch to operate.- In this instance -I4 find that I may obtain the utilization of this variation of resistance of the gases by connecting suitable means or apparatus in the circuit which includes the spark-plug.

have, therefore, in the drawings only shown contacts 7 and 8 as being employed. rThe spark-plug operates for both that is, for ig.-

- niting the mixtureand for taking advantage of the variations of resistance to the passagev of sparks between the two contacts.. l

It will be noted that upon the start of' the burner that there will be a supply of gas passing between the spark-plug contacts which supply is more or less pure air, and this will then be changed by the introduction of fuel in its vapo'rized state as it also issues from thepipei. The two intermixed gasesl passing'from the pipe 5 change the resistance to the passage of the sparks between points 7 and 8 from the resistance offered by the subsltantially. pure air. ance is reduced.-

When combustion takes place within has been found that some of the burning gases willA find their way back into thegcone 6 and these gases become mixed with? the gases issuing from pipe 5 and will thereby cause a different mixture of gases between the contacts 7 and 8. It has been found sa result` of experiment that under normal burn` inor conditions. that 4the gases between the points 7 and 8 offer lessfresistanceto the passage ofsparks between these points than the resi-stance oered by .substantially pure air passing from the pipe 5. It will be noted that when the resistance between points and 8 to the" passage of sparks is material there will be a relatively small flow of. ele-ctrical current through the primary winding lll) In this case the resistthe combustion chamber 4. vit

sparks between points 7 and 8 is less there will consequently be an increase of electrical current passing through thel winding 56 and through the winding of the electro-magnet 58. Under that condition the strength of mag- 'net 58 will be increased. I, therefore, take advantage of the resistance to the passage y of sparks between the points 7 and 8 for varytinue less than still closed, the burner line position noted in Fig.

ing the electrical control system which in turn controls'the operation ofthe burner.

In the operation of the device, assume that contacts 25 and 26 are closed and that the float feed switch 28 and the aquastat 34 are 1 will then be placed in operation or started upon the closing of the thermostat arm 31 on to contact 30. The closing of these'contacts completes the secondv ary Winding circuit through the transformer 2l and the electro-magnet 36 operates to close;

the contacts 44 and 45 thereby permittingthe burner motor 9 to start. Upon the closing 'of contacts 44 and 45 thespark coil becomes energized and likewise the electromagnet 58.

len the secondary winding 23 of the transformer 2l is closed there will be a larger flow primary circuit of the transformer and electro-magnet 22 will be flexible switch arm ori vmember 49 downward to maintain the conof current through the come active to pull the tacts 51 and 52 open.

As noted above, in the starting of the burner there will be a supply of air and of atomized fuel between and there will be a relatively high resistance and consequently electro-magnet-58 will exert a comparatively small force and will not pull the flexibleV lever 49 away from the influ-.

ence f electro-magnet 22 thereby closing the shunt circuit around the heat responsive safety switch..l

A In case the fuel .does not ignite at once the influence of electro-magnet 58 will still conthe influence of magnet 22 as there will be less current passing through the spark-plug circuit as the resistance to the passage of sparks between points 7 and 8 maintains the same, and current will then-pass through coil 41 of the heat responsive safety switch and will heat the metallic member 37. and cause it to rise to the dotted 3 and will thereby 'cause contacts 25A and 26 to separate, thus opening the circuit andstopping the operation yof the fuelburner. The burner may be again started onlyafter the manual opera-` tion of pulling catch 60 to 4Jthe right to permitcontactsk25 and 26 to returnl to engaging position.

Assume now, that upon the start ofthe "burner ignition takes place, the resistance of .quently the amount of the contacts 7 and 8 the gases between the contact points 7 and 8 will be decreased as above noted and consecurrent required to pass through winding 56 and through electro-magnet 58 will increase, and since electromagnets 58 and22 are designed in the proper manner to` balance against each other the magnet 58 now becomes predominating over magnet 22 and draws the flexible arm 49 upward to close contacts 51 and 52 thereby closing the shunt circuit around the heat responsive safety switch. In that condition the cur-A rent required for the operation of the burner motor then passes through conductor 38, winding'39, conductor 40, conductor 54, contacts 5l and 52, flexible arm 49, conductor 48 to contact 44 and from there back to terminall post 16 by means of conductor 47. The operation of" the burner will now continue normally until the thermostat opens and the burner automatically ceases operation.

Should the re or burning of theK gases in the combustion chamber 4 go out or cease for any reason there will the be a'higher resistance to the passage of sp ks between the Contact points 7 and 8 as noted above and con- '.sequently there will be a decrease of current 1n coil 56 and through magnet 58 causing magnet 22, to predominate over magnet 58 therebypulli'ng flexible arm 49 down and opening the shunt circuit around the heat responsive safety switch. As soon as this heat responsive safety switch has heated u'p as it by the utilization 'of the variation of conditions of mixture of the gas between electrical contact points suitably mounted in the combustion chamber of a fuel burner. If desired the same thoughtmay be expressed in detail in respect to the present disclosure by saying that the control of the fuel burner is responsive to the conditions of gases at the points of the spark-plug. It will be further notedy that this method of control gives a means for regulating theburner independent of the pressure or temperature existing in the combustion chamber and is dependent upon the resistance to the passage of electric sparks between two given contact points. In the particular disclosure I have utilized the electrical energy changeV` 1n the primary winding of spark coil transformer to vary or change the control system of the oil burner, andrin so doing I have, in the preferred disclosure, balancedone electro-magnetagainst another and arranged to have one of these electro-magnets ply. line fwill apply throughout the whole apparatus and therefore be compensated. It will be understood that while I have herein described 'in` detail ra particular embodiment of my invention for purposes of full disclosures and some detailed features which claiming for a special advantage, many changes and modifications may be made in the particular construction and arrangement of parts without departing from the broad scope of my invention. I claim fl. In combination, a liquid fuel burner, a combustion chamber therein for receiving a mixture of gases capable of combustion, elecand between them,

,erating the burner, means trical contacts positioned in said chamber and adapted to have the gases pass around an electrical control system for said burner,said system having included therein means vfor passing sparks across said contacts for igniting the mixture of gases, and another means in said electrical lsystem controlled bythe resistance oifered by the gases to the passing of sparks between said contacts whilethe sparking continues for varying'said electrical controll system to stop the operation of said burner.

2. In a fuel burner, means for operating the same, an electrical control system forgoverning the operation of said burner, contacts mounted within said burner and spaced apart so that electric sparks may pass from one contact to another, said contacts being mounted so that the gases within the burner may move into contact therewith and fill the space therebetween, and means in said electrical control system responsive to continuous high resistance of the gases trical control system to stop said burner.

3l In a liquid fuel burner,

for controlling the operation of said burner, a spark-plug in said controlling meansfor igniting the fuel,

" a combustion lchamberl I a mixture of gases capable of supporting com-- i60.. bastion, an electric said controlling means being responsive to the resistance offered by the gases in the burner to the' passing of sparks across the points of said plug while] theV sparking continues to vary the controlling means under `conditions of a continued high resistanceto stop said burner. l v

4L In combination, a liquid fuel burner,

therein. for receiving al system or controlling the operation ofsaid burner,'sparkplug terminals mounted in 'said combustion chamber and adapted to have thegasesv pass therebetween, said terminals being included in theA a transformer means in` said electrical system,

causing sparks to pass electrical system for throughy Iwhich sparking occurs for opening the elecmeans for oplstrength of saidmagnet for have its strength varied as the gases in said chamber resist the passage of sparks between said terminals, and a cut-out means also included in saidelectrical system and being controlled `by the variation in the strength of vsaid magnet and operating to vary said electrical system by opening the same when said magnet continues to exert relatively small strength. l j

5. In combination a liquid fuel burner, a combustion chamber therein adapted to receive a mixture of gases capable of supporting combustion, an electrical control circuit for. governing the. operation ofsaid burner, a spark-plug connected in said electrical circuit and adapted to ignite said combustible mixture; a heat responsive safety switch included within said electrical circuit and adapted to open said circuit after being heated to a predetermined temperature, means in said system for shunting said safety switch during normal operations of said burner, tem influenced by the resistance of the gases to the passage of sparks between the points of said spark-plug to open the shunt around said heat responsive safety switch to permit said switch to become operative.

6. In combination a liquid fuel burnera combustion chamber therein adapted to receive a mixture of gases capable of supporting combustion, an electrical control circuit for governing the operation of said burner, a spark-plug connected 1n said electrical circuit and adapted to ignite said combustible mixture, a heat responsive safety switch included in saidelectrical circuit and., adapted to open said circuit after being heated t o a predetermined temperature, a magnet included in the immediate spark-plug circuit, a switch in' the control circuit for shunting electric current around said heat responsive safety switch, said magnet normally ing the shunting `switch in closed position, and` means operating in opposition to the holding open said shunting switch when the v,energy required to pass sparks between the contacts ofsaid sparkplug against high resistance is substantially contant thereby permitting the heat responsive safety switch to `operate to sto-p the operations of, said burner.

holdlll lll

lll

ceive a mixture of combustible gases, means for operating lsaid burner; an electrical systemv for controlling the operation of said burner, a spark-plug mounted in association with said combustion chamber for igniting the combustible mixture, a subelectrical `circuit n said control system in which said spark-plug is fconnected, a magnet also connected in saidsubelectrical circuit and adapted to vary in strength in accordance with the resistance offered by the gases to the passage of sparks between the points of said sparkplug, a second sub-electric circuit in said control system, a magnet connected in said second subcircuit, a heat responsive safety switch connected in said control system, a shunt connection around said heat responsive safety switch, a flexible member carrying a contact to open and close the shunt circuit around said switch, said flexible member being mounted to be influenced by said magnets in opposite directions, said second magnet acting to maintain openy the shunt around saidheat responsive safety switch to permit said heat responsive safety switch to be actuated when the resistance of the gases to the passage of the sparks is constant and great to thereby open t-he control system to stopk the burner.,

8. In combination a liquid fuel burner, a combustion chamber therein for receiving a mixture of gases capable o f combustion, means for operating said burner, an electrical control system for said burner, \a sparkplug associated with said combustion chamber for igniting the mixture of gases, a transformer mounted in the control system yand having a magnet connected in the high volt'- age side thereof, burner control devices connected in tlie low side of said transformer, means in the high voltage circuit for impressing a potential across the terminals of saidspark-plug, a second magnet in the high voltage circuit of said control system, a heat responsive safety switch also mounted 4in the J'by said high voltage circuit of said control system, a circuit for shunting the passage of current around said heat responsive safety switch, a switch mounted in said shunt' circuit, said shunt circuit-switch adapted to be influenced magnets which arepositioned to\oppose the action of each other,said firstkmag; net becoming effective to open said shunt circuit when the resistance to kthe lpassage of sparks between the terminals of said sparkplug is abnormally hig 9. In combination, combustion chamber therein for receiving a mixture of gases capable of combustion, electrical contacts positioned in saidy chamber and adapted to have the gases pass around and between them, an electricalcontrol system for said burner said s stem havin said electrical contacts included therein, means in said control system for passing sparks across said contacts for igniting .the mixture of gases, another means in said electrical system affected by t-he gases, when unignited by the sparks, and offering relatively high re- Sistance to the passing of sparks betweensaid contacts while the sparking -continues for varying said electrical control system to stop the operation of said burner, and a thermostat responsive to heat conditions at a predeheat responsive safety said contacts-for gases,

a liquid fuell burnerla for operating said burner ina liquid fuel burner,

a combustion chamber therein for receiving a n mixture of gases capable of combustion, electrical contacts positioned in said chamber and adapted to have the gases pass aroundand between them, an electrical control system for said burner, said systemhaving said electrical contacts included therein, means iii said control system for passing sparks across igniting the mixture of gases, another means in said electrical system affected by the gases, when-unignited by theA sparks, and offering relatively high resistance to the passing of sparks between said contacts while the sparking continues, said other means adapted tovary said electrical control system to stop the operation of said burner, 'a thermostat responsive to heat conditions at a predetermined place for operating said burner intermittently, and safety devices in the velectric control system for preventing the operation of said burner when said thermostat closes if the burner is in alonormal condition.

11. In combination, a liquid fuel burner; a combustion chamber therein for receiving a mixture of gases capable of combustion, electrical contacts mounted in said Ichamber and adapted Ito have the gases pass around and between them, an electrical control system for said burner, said system having said electrical contacts included therein, meansfin said control system for passing sparks across said contacts for igniting the mixture: of a magnet connected in circuit with the spark passing means and capable of being excited to a greater or less degree due t the .variations in electrical current in said spark passing means caused bythe variations in resistance offered by the gases to the passage of sparks between said contacts, a heat respon'sive safety switch connected in said electrical contiol system which when actuated opens said control system and stops the los' flll) burner, a circuit in-'said system for shunting f said heat responsivesafety switch, a switch in said shunt circuit adapted to be influenced by said magnet to maintain closed said shunt circuit when the resistance of the gases tothe passage of sparks is relatively small, and a thermostat positioned to be responsive to heat conditions at a predetermined place and arranged to cause said burner to normally operate intermittently.

12. In combination,

a liquid fuel burner, a combustion chamber therein for receiving a mixture of gases capable of combustion,'

electrical contacts mounted in said chamber and adapted to have the gases pass around and between them, an tem for said burner, said system having said electrical contacts included therein, means in said control system for passing sparks across electrical control sysl gases, a magnet connected `in circuit with the spark passing means and capable of beingexcited to a greater or less degree due to the variations in electrical current in said spark passing means caused by the variations in resistance offered by the gases to the passage `of sparks between said contacts, a heat responsive safety switch connected in said electrical control system which when actuated opens said control system and stops the burner, a circuit in said system for shunting said heat responsive safety switch, a switch in said shunt 'circuit adapted to be influeneedby said magnet to maintain closed said shunt circuit whenthe resistance of the gases to the passage of sparks is relatively small, a thermostat positioned to be responsive to heat conditions at a predetermined place and arranged to cause ysaid burner to normally operate intermittently, and safety devices connected in series with said thermostat to prevent operation vof said burner when alonormal conditions exist. l 'y 13; ln a li uid fuel burner the combination ,of a combustion chamber, a spark-plug mounted in said chamber in the path of liquid fuel and air fed to said burner, an electrical control system for governing the oper'- ation `of said burner, a sub-electric circuit in said system for supplying current to said spark-plug, anLelectro-magnet in said subcircuit, the strength of said magnet being varied due to the variation in current flowing in said magnet in response to the resistance offered to the passing of sparks between the points of said spark-plug due to the variation in conductivity of the gases between the points of said spark-plug, a second subcircuit in said control system, a magnet'connected in said second subcircuit, a third subcircuit in said system, a heat responsive p safety switch mounted in said third subcircuit and adapt-ed to open the control system under abnormalv conditions of operation, a shunt circuit connected around said heat re` sponsive `safety switch, a flexible switch member mounted in said shunt circuit, said flexible switch member being responsive .to the Vdifferences of the pulls of said magnets, said flexible switch member adapted to be opened by said second magnet when the resistance to the passage of sparks between the points of said spark-plug is continuous and material thereby permitting current ,to low through said heat responsive safety switch causing the same to open saidl electric control systeml and stop the operation of said burner.

14. In combination, an operating appara.- tus having a' varying mixture of gases therein during operation, and electrical means for controlling the operation of said apparatus, said electrical means having included therein electrical contacts mounted in spaced relation to form a spark gap and being positioned in the path of said gases, said electrical means adapted to be varied by the changes in the resistance to the passage of sparks between said contacts due to the variations in the electrical conductivity of said gases to maintain continuation of operation of said apparatus under predetermined conditions and to stop said operations under other conditions.

15. In combination, an operating apparavtus having a Varying mixture of gases therein during operation, and electrical means for controlling the operation of said apparatus, said electrical means having included therein electrical contacts mounted in spaced relation to form a spark gap and being positioned in the path of said gases, said electrical means adapted to be varied by the changes in the resistance to the passage of sparks between said contacts due to the variations in the electrical conductivity of said gases to maintain continuation of operation of said apparatus unf derpredetermined conditions and to stop said operations unde other conditions, andmeansj in said electrical control system being brought into operation when the resistance to the passage of `sparks between said conmaintaining the passage of sparks across a gapV located in the combustion area of the burner, and controlling the operation of the burner in response to the lesser resistance offered by the gases at the gap to the passing of said sparks across said gap when thereis combustion of said'gases than when there is no combustion thereof. v

Thisu specification signed this 5th day of May, 1926.

ROBERT s. METCALFE. 

